1. Field of the Invention (Technical Field)
The present invention relates generally to the field of direct deposition of passive structures. More specifically, the invention relates to the field of maskless, precision deposition of mesoscale passive structures onto planar or non-planar targets, with an emphasis on deposition of precision resistive structures.
2. Background Art
Note that the following discussion refers to a number of publications and references. Discussion of such publications herein is given for more complete background of the scientific principles and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Various methods for deposition of passive structures exist, however, thick film and thin film methods have played a dominant role in the deposition of passive structures, including but not limited to resistors or capacitors, onto various electronic and microelectronic targets. By way of example, the thick film technique typically uses a screen-printing process to deposit electronic pastes with linewidths as small as 100 microns. Thin film methods for the printing of electronic structures include vapor deposition techniques, such as chemical vapor deposition and laser-assisted chemical vapor deposition, as well as physical deposition techniques, such as sputtering and evaporation.
U.S. Pat. No. 4,938,997 discloses a method for the fabrication of thick film resistors on ceramic substrates, with tolerances consistent with those required for microelectronic circuitry. In this method, a ruthenium-based resistor material is screen printed onto the substrate and fired at temperatures in excess of 850° C. U.S. Pat. No. 6,709,944 discloses a method for fabrication of passive structures on flexible substrates by using ion bombardment to activate the surface of a substrate such as polyimide, forming a graphite-like carbon region that may be combined with another deposited material—such as titanium—to form a passive structure. U.S. Pat. No. 6,713,399 discloses a method for the fabrication of embedded resistors on printed circuit boards. The method uses a thin film process to form embedded passive structures in recesses that have been formed in a conductive layer. The method of U.S. Pat. No. 6,713,399 discloses a process that eliminates the high resistance variation seen in polymer thick film embedded resistors.
While thick film and thin film methods of passive structure fabrication are well-developed, these processes may be unsuitable for certain deposition applications. Some disadvantages of thick film processes are the relatively large minimum linewidths that are characteristic of the technique, the need for mask utilization, and the need for high-temperature processing of the deposited material. The disadvantages of typical thin film processes include the need to use masks, vacuum atmospheres, and multi-step photolithographic processes.
In contrast with conventional methods for deposition of passive structures, the M3D® process is a direct printing technique that does not require the use of vacuum chambers, masks, or extensive post-deposition processing. Commonly-owned International Patent Application Number PCT/US01/14841, published as WO 02/04698 and incorporated herein by reference, discloses a method for using an aerosol jet to deposit passive structures onto various targets, but gives no provision for lowering the tolerance of deposited structures to levels that are acceptable for manufacturing of electronic components. Indeed, the use of a virtual impactor in the invention disclosed therein eventually leads to failure of the system due to the accumulation of particles in the interior of the device. As a result, the maximum runtime before failure of the previously disclosed system is 15 to 100 minutes, with the electrical tolerances of deposited structures of approximately 10% to 30%.
Contrastingly, the present invention can deposit passive structures with conductance, resistance, capacitance, or inductance values with tolerances of less than 5%, and runtimes of several hours.